The production of a specified magnetic flux within a given working volume has conventionally required an assembly of magnets positioned so as to define the working volume, a ferromagnetic structure (called a yoke) of high magnetic permeability to provide a low-reluctance (i.e., low "magnetic resistance") path for the flux to and from the magnets, and poletips of low reluctance and high permeability to the distribute the flux over the working volume. Efficiency in the use of ferromagnetic materials from the standpoint of weight (and therefore cost) has conventionally required that the magnets be placed immediately adjacent the working volume, and that the poletips be used to transport the flux into the working volume. Generally, attempts in the prior art to decrease yoke weight have resulted in an increase in magnetic leakage flux (stray flux) due to loss of the yoke's shielding effect.
A dipole magnetic assembly designed for use as a focussing lens or collimator for kinescopes was described by K.K.N. Chang in "An Analytic Solution of a Magnetic Electron-Beam Bender", RCA Review, Vol. 42, pp. 111-117, (March 1981). Other applications of a commercial nature for dipole magnetic assemblies were described by K.K.N. Chang in "Collimated Electron Trajectory in a Nonuniform Transverse Magnetic Field", RCA Review, Vol. 40, pp. 390-396, (December 1979), and by D. Gabor in U.S. Pat. No. 2,872,607.
A dipole magnetic assembly (referred to as a "Watson magnet") for use in biasing computer bubble memories was described by D. S. Bartran and L. G. Chow in "An Analysis of Magnetic Fields Encountered Between Two Permeable Sheets", IEEE Transactions on Magnetics, Vol. MAG-10, No. 2, pp. 379-381, (June 1974).